Some embodiments relate generally to the field of material durability and more specifically to the assessment of chloride concentration in porous and composite materials, such as reinforced concrete, pre-stressed concrete or mixed steel-concrete structures. More particularly, some embodiments relate to a system and a method for assessing chloride concentration in a predetermined area of a porous or composite material and to a sensor used in this system and method.
Chloride ingress is one of the major factors of reinforced concrete (RC) deterioration affecting structural serviceability and safety. Chloride ions are accelerators of corrosion processes on the rebar surfaces, decreasing the lifetime of the structures. For other materials, the detection of chlorides is an indicator of the waterproofing against seawater or material durability.
Chloride-induced corrosion begins when the concentration of chloride at the steel bars reaches a threshold value that destroys a thin passive layer of corrosion products (caused by the high alkalinity of concrete at the end of construction), which protects steel bars against corrosion. After corrosion initiation, there is a premature deterioration caused by various mechanisms: loss of reinforcement section, loss of steel-concrete bond, concrete cracking and delamination. After steel corrosion starts, the RC physical and mechanical properties decay at rate that depends on the environmental conditions. This deterioration process generates larger repair and maintenance costs with severe impact on the durability and life-cycle performance.
The measurement of chloride content at the concrete cover could be used to estimate the risk of corrosion initiation, and therefore, to enhance or optimize repair and maintenance costs.
The ingress phenomenon of the chloride ions into the concrete is very complex since it depends on many parameters, notably the concrete composition, its cracking state and the climate to which it is exposed.